1. Field of the Invention
The present invention relates to a platform weighing apparatus of the general type that includes a stationary base platform and a load supporting platform. The supporting platform is mounted for vertical reciprocal movement toward and away from the base platform when a load is positioned on it.
Platform weighing apparatus of this general type have great utility in heavy industrial applications. They may, for example, be used to weigh large objects such as loaded hand trucks or other large containers of heavy material. However, such apparatus may also be adapted for lighter load weighing applications.
2. Description of the Prior Art
Common platform weighing apparatus of the type to which this invention relates include a base platform of square or rectangular shape. Ordinarily, four load measuring devices such as hydraulic load cells or electric strain gauges are mounted on the base platform at each of its corners. A load supporting platform, of shape similar to the base platform, is then mounted above the base platform, supported by the load measuring devices. Accordingly, when a load is placed on the supporting platform it produces an output signal from the load measuring devices by physical movement of the supporting platform relative to the base platform. Such movement will increase the hydraulic fluid pressure in a hydraulic load cell or cause an electric strain gauge to generate an electric output signal as an indication of the measured load.
Linkages are also provided between the base and load supporting platforms that permit relative vertical movement but resist horizontal movement therebetween.
Because the load is often not placed in the physical or dynamic center of the load supporting platform, different ones of the load measuring devices may produce different output signals. Therefore, a totalizer device may be used to total the output signals of the several load measuring devices and produce a single output signal indicative of the actual weight of the load.
U.S. Pat. No. 3,933,212 (Bradley et al.) discloses a high capacity platform weighing apparatus of the general type described above and U.S. Pat. No. 4,078,624 (Bradley) discloses as similar apparatus that is, however, of modular construction. In each, when the apparatus is assembled, stabilizing linkages extend between the load supporting and base platforms parallel to and adjacent each edge of both platforms. Each linkage operates independently of the other three.
Another weighing apparatus of the type generally described above is disclosed in U.S. Pat. No. 2,742,278 (Carleton, Jr.) and includes a base platform, a middle-scale platform and an upper-scale platform mounted above the middle-scale platform. The upper-scale platform is supported above to the base platform at each of its four corners by one of four electric load cells. The middle-scale platform is connected to the base platform by four tie or stabilizer rods or linkages, each of which extends parallel to and adjacent one edge of the platforms. Limited vertical movement is permitted between the middle-scale platform and the base platform by slight bending of each tie rod. Again, however, each tie rod may be bent independently of bending of other rods.
U.S. Pat. No. 3,658,143 (Schwartz) discloses a weighing device in which a load supporting platform is linked to a single load measuring device by a lever system that incorporates flexure plates and flexible cables.
Still other platform weighing devices are shown in U.S. Pat. Nos. 3,354,973 (Farquhar); 4,064,955 (Dyck) and 3,338,324 (Burke et al.).